This invention relates to devices used to cover or seal storm drain grates or similar apertured drain members when it is desired to prevent liquids from passing through the grates into the drain system. More particularly, the invention relates to such devices which comprise liquid impermeable mats or sheets composed of polymeric materials, where the mats are simply placed onto the top of the grates to close off the openings.
Drainage systems for removing liquids from an area are well known, and may comprise for example storm drain systems for removing rain water from roads and parking lots or interior drain systems provided in the floors of warehouses and other buildings. In many such systems the drain system comprises an interconnected network of pipes or other conduits which receive water flowing through surface mounted drains and deliver the water to a reservoir or tank, or deliver the water to a remote exterior location for release. The drains are usually provided with an apertured grate, such that liquids will freely pass through the grate but large objects will be precluded from entering in order to prevent blockage of the drain system, lost objects and accidental injury. The grates are of many configurations and may be rectangular, square, circular, etc., and the individual openings or apertures in the grates themselves may be of many shapes, such as circular, square, rectangular, etc., as there is no uniform or standard configuration within the industry.
Under certain circumstances it is desirable to quickly seal the drains such that liquid does not pass into the drain system, since in many instances the drain systems simply release liquids into the environment at remote or controlled local locations. For example, it may be necessary to temporarily seal the drains when pollutants or hazardous material spills occur, due for example to tanker truck accidents, pipe or liquid container failures, etc., in order to prevent the hazardous liquid from passing into the drain system and out into the environment. It is known to provide mechanical valves or custom fitted caps which correspond to a particular grate design, but these solutions are not viable in many circumstances, such as with outdoor storm drain systems where various designs of grates may be encountered, and are not particularly suitable in emergency situations where an immediate response is required. It is more practical to have a drain seal which operates in a universal and simple manner, such that a large variety of grates can be quickly and effectively sealed by response personnel without the need to match a particular grate or to undertake excessive, time-consuming connection steps.
To this end drain sealing devices have been developed which comprise in general a sheet or mat composed of a flexible polymeric or elastomeric material, the material being impermeable to liquids and highly chemical resistant, such that the drain can be sealed by placing a mat directly on, top of the grate, where the mat's outer dimensions extend beyond the outer edges of the grate. Such sealing devices may be composed of polyurethane, PVC, silicone or other polymers possessing appropriate properties.
One example of such a sealing device is a drain seal sold commercially under the brand name DRAINBLOCKER by New Pig Corp., which comprises a flexible, two-layer, polyurethane mat having a thin upper structural layer made of polymer coextensively joined to a thicker lower sealing layer made of polymer, where the upper structural layer is denser, less elastic, and less flexible than the lower layer. The lower sealing layer is somewhat tacky and is provided on the underside with a thin, removable cover layer which is removed prior to use. In use, the soft lower layer conforms and seals against the grate and the surrounding frame, roadway or floor slab such that liquids cannot pass beneath the drain seal and into the drain. The upper structural layer is provided to impart strength and increased rigidity to the lower layer, and to prevent tearing during handling. Such a drain seal suffers from several inherent weaknesses, including the need to provide a removable cover layer to prevent undesirable adhesion to other mats and other objects during storage, and to prevent accumulation of debris, dust, sand and other particulate matter on the soft lower layer prior to use, which cover layer needs to be reapplied to the sealing device after it is cleaned for reuse. Another drawback is the coextensive upper structural layer impedes the sealing efficiency of the soft lower layer. Another drawback is the problem of incorrect use of the sealing device, since response personnel may easily invert the device in an emergency response such that the structural layer is mistakenly placed directly against the grate rather than the softer sealing layer, in which case the drain may not be properly sealed. In addition, larger mats of this design are subject to tearing because of the lack of internal structure or reinforcement, such that a small tear in the perimeter rapidly passes through the entire mat during handling.
Another example of a sealing device in the form of a mat is shown in U.S. Pat. No. 4,988,234 issued to Henkel et al. This device is similar to the New Pig device described above and comprises a flexible two-layer mat where the thin upper layer is denser and less elastic than the lower layer. The upper layer is shown to comprise a silicon rubber and the lower layer is described as a molding composition which comprises a highly viscous, sticky, silicone gel. The sealing device must remain sealed in an air-tight package until needed for use. The gel cures from a plastic state into an elastic state when exposed to moisture in the atmosphere, such that when the device is placed onto a grate to prevent liquid passage into the drain system, the lower gel layer freely flows to enter and fill the grate apertures, whereupon it quickly cures to adopt a configuration particular to that grate. Such a sealing device is therefore not reusable and is difficult to handle during emergency situations, since the device must first be removed from the air-tight packaging, and is likewise susceptible to tearing and failure due to the lack of internal reinforcing structure, as well as inversion by inexperienced personnel.
Still another example of a drain sealing device is the sealing mat of U.S. Pat. No. 4,838,732 issued to Clark et al. This device comprises a core elastomer having low shear resistance and high flow characteristics, with the core elastomer being encased in a flexible, thin-film, liquid impermeable envelope, which may be open or sealed on the edges. Drawbacks to this device include the tendency of the flowable core elastomer to bottom out during storage due to gravity effects, such that the core elastomer may be unevenly distributed within the device unless the device is stored in a flat position. Also, since the envelope material contacts the ground and grate surfaces rather than the softer core elastomer, there is less adhesion and a greater likelihood that liquid flowing against the mat will lift the edges of the mat and enter the drain system. As with the other sealing devices described above, there is no reinforcing structure, such that the mat is susceptible to tearing and failure.
Another example of a drain sealing device is shown in our U.S. Pat. No. 6,530,722, which shows a sealing mat composed of a polymeric material and having an internal reinforcing scrim or similar reinforcement members disposed internally. The polymeric material has a sufficient minimum amount of creep or flexibility such that all of the apertures in the grate are well sealed by contact with the underside of the device, while the reinforcing material adds structural integrity and durability to the device. A drawback to this device is that the exposed upper surface is susceptible to damage from vehicular traffic.
It is an object of this invention to address and overcome the problems and drawbacks inherent in the known mat-type drain sealing devices by providing a drain sealing mat device which is a multi-layer mat, one layer being composed of polymeric material, where the semi-rigidity of the polymeric material provides a suitable amount of creep or sag such that the layer will conform to the apertures in the grate to be sealed without such creep or sag being excessive, and with the other layer being composed of a polymeric material of different properties, this upper layer being more rigid and durable so as to provide protection to the lower layer, with the layers not joined coextensively but instead connected at a relatively small number of discrete points or regions such that the creeping or sagging of the lower layer is not impeded or restrained by the non-creeping upper layer. These objects and other objects not expressly stated will be made evident upon examination of the disclosure which follows.